Problem solved. After looking around a lot and googling through different pages I found the answer. I'll leave the link in case someone else has the same problem (search for deep level numbering instead of numbered list):
http://www.syncfusion.com/support/kb/289/How-to-create-the-deep-level-numbering%28-11-121-122-etc%29-using-DocIOC#
ListStyle styleN = document.AddListStyle(ListType.Numbered, "ListStyleN");
WListLevel listLevelL0 = styleN.Levels[0];
listLevelL0.CharacterFormat.FontSize = 16;
listLevelL0.CharacterFormat.Bold = true;
listLevelL0.CharacterFormat.Italic = true;
listLevelL0.ParagraphFormat.LeftIndent = 0;
listLevelL0.ParagraphFormat.FirstLineIndent = 20;
WListLevel listLevelL1 = styleN.Levels[1];
listLevelL1.IsLegalStyleNumbering = true;
//Numberprefix defines prefix before numbering.
//\x0000 - defines that numbering of the previous level will be inherited
listLevelL1.NumberPrefix = "\x0000.";
listLevelL1.ParagraphFormat.LeftIndent = 70;
listLevelL1.ParagraphFormat.FirstLineIndent = -10;
WListLevel listLevelL2 = styleN.Levels[2];
listLevelL2.IsLegalStyleNumbering = true;
//\x0000.\x0001. - inherirs numbering of level 0 and 1
listLevelL2.NumberPrefix = "\x0000.\x0001.";
listLevelL2.ParagraphFormat.LeftIndent = 130;
listLevelL2.ParagraphFormat.FirstLineIndent = -40;
VB
Dim styleN As ListStyle = document.AddListStyle(ListType.Numbered, "ListStyleN")
Dim listLevelL0 As WListLevel = styleN.Levels(0)
listLevelL0.CharacterFormat.FontSize = 16
listLevelL0.CharacterFormat.Bold = True
listLevelL0.CharacterFormat.Italic = True
listLevelL0.ParagraphFormat.LeftIndent = 0
listLevelL0.ParagraphFormat.FirstLineIndent = 20
Dim listLevelL1 As WListLevel = styleN.Levels(1)
listLevelL1.IsLegalStyleNumbering = True
''Numberprefix defines prefix before numbering.
''\x0000 - defines that numbering of the previous level will be inherited
listLevelL1.NumberPrefix = ChrW(&H0000).ToString() & "."
listLevelL1.ParagraphFormat.LeftIndent = 70
listLevelL1.ParagraphFormat.FirstLineIndent = -10
Dim listLevelL2 As WListLevel = styleN.Levels(2)
listLevelL2.IsLegalStyleNumbering = True
''\x0000.\x0001. - inherirs numbering of level 0 and 1
listLevelL2.NumberPrefix = ChrW(&H0000).ToString() & "." & ChrW(&H0001).ToString() & "."
listLevelL2.ParagraphFormat.LeftIndent = 130
listLevelL2.ParagraphFormat.FirstLineIndent = -40